1. Field of the Invention
This invention is directed to a process. More specifically, this invention involves a novel process for vapor phase cracking of dicyclopentadiene and the synthesis of 2,3-dihydrodicyclopentadiene therefrom.
2. Description of the Prior Art
Dicyclopentadienes are of significant industrial value because of their ready conversion to either polymers or as intermediates in the preparation of a variety of desirable products (e.g. cyclopentadiene or cyclopentene). Dicyclopentadiene has been previously disclosed as a starting material in the synthesis of cyclopentene, U.S. Pat. No. 3,598,877. The '877 patent and the prior art discussed within patentees' specification teach that cracking of dimeric cyclopentadiene can take place in the presence of an auxiliary liquid, or in the vapor phase (with or without a hydrocarbon diluent). The presence of the auxiliary liquid during cracking of the dimer can adversely effect the yield. Because of such difficulties, industrial scale manufacture of monomeric cyclopentadiene is carried out via a vapor phase process. Such industrial processes will generally involve the vaporization of the dimer and conveyance of the resultant gaseous fluid through a heated tubular reactor wherein cracking to the monomer occurs. Since such depolymerization is reversible, even at low temperatures, the monomer must be fractionated rapidly if reasonable quantities of monomer are to be recovered.
Vapor phase cracking of cyclopentadiene dimer and higher polymers result in a greater conversion to the monomer, as compared to liquid phase cracking. However, there are serious drawbacks associated with vapor phase cracking; namely, the formation of coke on the interior walls of the cracking tubes. Inert gas addition to the vaporized dimer has been proposed to alleviate this difficulty, although Nelson et al (U.S. Pat. No. 2,801,270) indicated that the process may be operated efficiently without such inert gas addition, and that such addition may actually hinder the separation of the monomer from the other materials in the cracking reactor effluent.
The inventors of the process of patent '877 indicate that coke formation can be minimized during vapor phase cracking of cyclopentadiene dimer by the addition of a hydrocarbon diluent to the dicyclopentadiene feedstock. The hydrocarbon diluents suggested by patentees must satisfy very specific requirements regarding their inertness and heat of vaporization.
As is evident from the above discussion, vapor phase cracking of dicyclopentadiene is the more desirable of the other alternatives disclosed by the prior art insofar as the yields obtainable are more commercially acceptable. There is, however, the continuing problem of coincident coke formation within the cracking apparatus. The invention described in the '877 patent is significant in the sense that it goes a long way toward reducing coke formation, however, with the added disadvantage of introduction of materials into the feedstock which create downstream problems regarding their separation from the desired end product.